Existing conductive intermediates (such as ruthenium dioxide, silver/palladium solid solutions, and bismuth ruthenate) combined with non-lead frits can form the low-resistance end of an essentially lead-free resistor system (10 to 1000 ohms), while existing conductives (such as ruthenium dioxide, bismuth ruthenate and strontium ruthenate) with non-lead frits could be used to make a 10 kilohm member. Ceramic resistor systems commonly include individual decade members which range between 10 ohms/square and 1 megohm/square. Resistors in these series must be insensitive enough to variations in thermal process conditions to be used on high speed manufacturing lines. Currently, most commercial resistor systems in the 100 kilohm to 1 megohm range utilize lead-containing frits and/or lead-containing conductive phases, such as formulations containing either lead ruthenate, or RuO2 and high-lead frits.
Fukaya and Matsuo (1997, 97 ISHM Symposia Proceedings, pp. 65-71) describe a RuO2/sodium alkaline-earth alumino-borosilicate frit resistor system that can be fired on alumina substrates or an LTCC system as described therein. The resistance of the system extends generally from 10 ohms to 500 kilohms. ±100 ppm/° C. TCRs are reported from 100 ohms to 500 kilohms.
Hormadaly (2002, 02 IMAPS Symposia Proceedings, pp. 543-547) describes resistors composed of M2−xCuxRuO7−β, where x is 0.2 to 0.4, β is 0 to 1, and M is a rare earth element. An example of a 6.15 megohm thick-film resistor is given.
Atsushi et al (2002, JP 2002-101903) describe a resistor composed of RuO2 and a bismuth-bearing frit with or without bismuth ruthenate.
JP 2003-197405 describes RuO2 and several ruthenates (such as CaRuO3) combined with frits composed of many alkali and alkaline-earth borosilicates, and many transition metal drivers.
There nevertheless remains a need to find a non-lead conductive-oxide/frit combination that could provide resistor compositions in the 100 kilohm to 10 megohm range, and preferably with ±100 ppm/° C. TCRs.